Numerous processes are available for production of lubricating oil basestocks from oil fractions. Such processes often involve hydroprocessing some type of oil fraction, such as hydrotreating or hydroconversion of the raffinate from a solvent extraction, followed by dewaxing of the hydroprocessed fraction. A hydrofinishing step of some type is also typical to improve the properties of the resulting lube basestock.
One method of classifying lubricating oil basestocks is that used by the American Petroleum Institute (API). API Group II basestocks have a saturates content of 90 wt % or greater, a sulfur content of not more than 0.03 wt % and a VI greater than 80 but less than 120. API Group III basestocks are the same as Group II basestocks except that the VI is at least 120. A process scheme such as the one detailed above is typically suitable for production of Group II and Group III basestocks from an appropriate feed.
Unfortunately, conventional methods for producing a lube basestock are hindered due to differing sensitivities for the catalysts involved in the various stages. This limits the selection of feeds which are potentially suitable for use in forming Group II or higher basestocks. In conventional processing, the catalysts used for the initial hydroprocessing of the oil fraction often have a relatively high tolerance for contaminants such as sulfur or nitrogen. By contrast, catalysts for catalytic dewaxing usually suffer from a low tolerance for contaminants. In particular, dewaxing catalysts that are intended to operate primarily by isomerization are typically quite sensitive to the amount of sulfur and/or nitrogen present in a feed. If contaminants are present, the activity and selectivity of the dewaxing catalyst will be reduced.
To accommodate the differing tolerances of the catalysts involved in lube basestock production, the following features are typically incorporated into the basestock production process. First, the hydroprocessing step (such as raffinate hydroconversion) is run under sufficiently severe conditions to convert most of the organic sulfur and nitrogen in the feed into volatile compounds, such as H2S and NH3. Second, a separation step is used between the hydroprocessing step and the dewaxing step which removes substantially all of these contaminants prior to the dewaxing step. The separation step requires extra equipment to be used during the lube production, which increases the overall cost of the process. Additionally, the hydroprocessing step may have to be run for converting the contaminants to a gaseous form under more severe conditions than otherwise needed to meet the lube basestock specifications such as viscosity, viscosity index, and sulfur content. Hence, there is a need for improved catalytic dewaxing processes and catalysts for use in such processes that eliminates the need for a separation step between the hydroprocessing process and the dewaxing process, and thus minimizes yield loss due to overconverting the lube feedstock in the hydroprocessing step for producing Group II and III lubricant basestocks from raffinates, hydrocracker bottoms or waxy feeds. Dewaxed lube oil yield is also maximized in the dewaxing zone.